The preferred embodiment concerns a method and a device to convert color-describing input data suitable for graphical output with the aid of an output apparatus into color-describing output data. Conversion methods are known to convert RGB input data displayable with the aid of a monitor into CMYK output data that can then be output with the aid of a typical printer. A conversion of color data of a first color model into color data of a second color model thus occurs in this known method. The primary colors of the RGB color model are red, green and blue. The colors of the CMYK color model are cyan, magenta, yellow and black wherein the color black serves as a contrast color (what is known as a key color) in color mixtures of the color model.
Subtractive and/or additive color mixtures can be generated with the aid of the primary colors of the respective color model, wherein a color space is defined by the generatable mixture colors. Given typical multicolor printing, the individual primary colors are not mixed but rather are printed in succession in what are known as color separations on the substrate material to be printed or an intermediate image carrier to collect the color separations. A color separation that defines the regions of the print image to be generated that are to be inked with this primary color is generated for each of the primary colors. The individual color separations are advantageously printed slightly offset from one another in a point raster (what is known as a print raster), whereby each color point comprises one pixel of the primary colors used to generate the color point.
The different principles of color mixing in monitor display and in the printing process (in particular in electrophotographic printing) makes it necessary to convert the image data generated or processed on the monitor on the basis of the RGB color model into image data of the CMYK color model. What are known as profiles in which a mixed color of the original color model is associated with a mixed color of the target color model are used for such a conversion. These profiles typically comprise tables with a plurality of color associations of mixed colors of the origin system and mixed colors of the target system. For specific output apparatuses, these profiles can be adapted to the output apparatus. Such an adaptation is also designated as a color calibration and can be implemented with what are known as color management systems (CMS). Such color management systems serve for color calibration of peripheral apparatuses that participate in a color processing. Such apparatuses are in particular cameras, scanners, monitors and color printers.
A correction 10 of the apparatus-specific color corruptions that conforms the color tones of (for instance) a scanned image, the monitor and a printout occurs via the adaptation of the profiles. It is thereby possible to define the color data in an apparatus-independent color space such as the LAB or CIELAB color space, and then to convert these in the apparatus-independent color space into the apparatus-dependent color space. Standards for the format of such apparatus profiles are developed and published by the International Color Consortium (ICC), for example. Specific apparatus profiles that can be used on various operating systems and user platforms can be generated with the aid of such ICC-conformant profiles. Images can thereby be transferred from one operating system to another operating system without having to change the apparatus profile.
Each apparatus has an apparatus-specific color space that is defined by a coordinate system in which an axis of the coordinate system is associated with each primary color. Every point in this color space defines a specific color. Typical in practice are: the RGB color space for monitors according to the aforementioned RGB color model; the CMYK color space for printers according to the mentioned CMYK color model; the HSB color space according to the HSB color model (hue, saturation, brightness); and the CIELAB color space defined by the Commision Internationale de L'éclairage (International Commission on Illumination=CIE), which is a standardized, idealized color space that numerically describes all colors that a person can perceive.
In the prior art, the output apparatus with the aid of which an image corresponding to the output data is output must already be established in the color conversion and in the color management. An adaptation of the color-describing output data to specific (in particular modified) output properties of a concrete output apparatus are then no longer possible in the prior art.